I upgraded the App Center to 0.2.3, but then the site, http://packages.elementary.io/appcenter, the packages are hosted on is reporting a bad gateway. The App Center isn't showing anything other than the default apps that come with my fresh install of Elementary OS.
When running sudo apt-get update && sudo apt-get upgrade I get the error:
Reading package lists... Done ... E: Failed to fetch http://packages.elementary.io/appcenter/dists/xenial/main/binary-amd64/Packages 521 Origin Down [IP: 22.214.171.124 80] E: Some index files failed to download. They have been ignored, or old ones used instead.